Narrow Results

The one-loop effective energy density of a pure SU(2) Yang–Mills theory in the Savvidy background is reconsidered. The stable and the unstable modes are identified. The stable modes are treated in the quadratic approximation. For the unstable modes, the full expansion including the cubic and the quartic terms in the fluctuations is used. The functional integral for the unstable modes is evaluated and added to the result for the stable modes. The resulting energy density coincides with the real part in the quadratic approximation of earlier studies and there is now no imaginary part.